Move comment in FlagSet definition
Move comment in FlagSet definition

The comment about how the flag union "|" operation is actually
(somewhat of) an intersection belongs with the method definition,
as opposed to the class definition.

dotty-staging/dotty,sjrd/dotty,lampepfl/dotty,dotty-staging/dotty,sjrd/dotty,lampepfl/dotty,sjrd/dotty,dotty-staging/dotty,sjrd/dotty,som-snytt/dotty,sjrd/dotty,som-snytt/dotty,lampepfl/dotty,dotty-staging/dotty,dotty-staging/dotty,som-snytt/dotty,lampepfl/dotty,lampepfl/dotty,som-snytt/dotty,som-snytt/dotty